Highly-Ordered Ultrathin Pd Films on Pt(111): Electrodeposition and Structural Characterization

Abstract

The present manuscript describes the preparation, surface characterization, and interfacial electrochemistry of ultrathin Pd films, from submonolayer to multilayer coverages, electrodeposited on well-defined Pt(111) surfaces. Between the coverage regimes studied, the growth of the films followed the Stranski-Krastanov mechanism.The interfacial electrochemical properties associated with the film-to-bulk transition were characterized by voltammetric techniques in combination with low-energy electron diffraction and Auger electron spectroscopy. It was found that the Pd electrodeposit started to exhibit bulk-like properties at three monolayers.Voltammetric cycling, between the hydrogen evolution and the double-layer regions, was found to exert minimal influence on the smoothening of the electrodeposited films. However, cycling within the same potential region in the presence of bromide anions (at which Br -adsorption/Br desorption takes place) considerably smoothened the initially rough Pd films, comparable to hightemperature annealing.The influence of chemisorbed bromine on the anodic dissolution of Pd was also studied. The present studies indicated that bromine was desorbed along with the dissolution of the Pd step-atoms in a manner that may be described as electrochemical digital etching. IntroductionUltrathin metallic films on foreign metal surfaces exhibit surface phenomena that are of significant interest in catalysis (1-3) and magneto-optics (4-6). The choice of the filmsubstrate combination is essentially determined by the intended resultant properties. For instance, the quest for high-performing fuel cell catalysts has stimulated investigations on the use of multimetallic films to improve the catalytic action and CO-poisoning tolerance of Pt (7). Another illustrative example is the surface modification of Au, Pt, Pd, and Cu substrates by the deposition of ultrathin layers of ferromagnetic metals (for examples see to create well-defined superstructures that can be incorporated in memory storage devices. In all these cases, the desired properties of the prepared material are highly dependent on surface coverage of the ultrathin metallic film. Establishing preparation methods that not only allow precise film-thickness control but also satisfy ECS Transactions, 3 (34) 65-103 (2007) 10.1149/1.2795613, copyright The Electrochemical Society 65 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 141.211.4.224 Downloaded on 2015-07-13 to IP 66 both technological demands and fundamental scientific interest remains an active research endeavor.Deposition methods for the Pt-group metals classically involve ultrahigh vacuum (UHV) conditions that effectively minimize contamination and allow surface characterization (13,14). However, for ultrathin films whose function or application involves solid-liquid interfaces, such as electrocatalysts and protective coatings, the films are best prepared and characterized in situ. In this regard, electrochemica...

Interfacial Structure and Chemistry of Potentiodynamically Electrodeposited Ultrathin Pd Films on Pt(111)

“…The Pt peak for Pd PSD films is indiscernible at 3 ML. These spectral features are very similar to those for Pd CPD films with corresponding Pd coverages (8).…”

“…(iv) As the Pd coverage increases from 1 to 4 ML, a concomitant increase in the total H upd desorption charge is observed. The aforestated trend differs with the behavior of Pd CPD films of corresponding coverages (8).…”

“…Recently, our group examined the interfacial properties of ultrathin Pd films prepared by constant potential deposition (CPD), hereafter referred to as Pd CPD films, on Pt(111) (8). In the present paper, we investigate how the structural and electrochemical properties of ultrathin Pd films are influenced by continuous potential ECS Transactions, 19 (24) 25-42 (2009) perturbation.…”

“…Recent studies on the electrodeposition of Pd on Pt(111) revealed evidences of a pseudomorphic Stranski-Krastanov growth mode (8)(9)(10). The growth mode and morphology of Pd thin films were found to be very sensitive to electrodeposition conditions such as overpotential and electrolyte composition (10,11).…”

Hydrogen Adsorption, Absorption, and Desorption at Palladium Nanofilms formed on Au(111) by Electrochemical Atomic Layer Deposition (E-ALD): Studies using Voltammetry and In Situ Scanning Tunneling Microscopy

“…Electrochemical annealing is generally performed at potentials near the start of surface reactions such as oxidation or the HER, where exchange currents are high and surface mobility promoted, producing results analogous to those generally observed with the increase in surface diffusion accompanying an increase in temperature for surfaces in vacuum. 83,84 In addition, adsorbates can promote electrochemical annealing by coordinating with surface atoms, resulting in significant surface and electronic changes. 85−88 Initially, 20 CVs in 0.1 M H 2 SO 4 at 10 mV/s between 0.1 and 0.5 V, where no significant voltammetric features were observed, were employed on a 15 E-ALD cycle Pd film.…”